Error indexing usig logicals

Hi there, I have an issue while using logicals for change the size of a vector: here's a simple code test:

rad = 0.3;
A = linspace(0,1,51);

nn = A(A <= 3*rad);
n2 = A(A <= 0.9);

Normally size(nn) has to be equal to size(n2), but nope... I'm kind of lost. Does anyone have an idea what's going on here?

[Stephen23]

"Error indexing usig logicals"

There is no error.

" Does anyone have an idea what's going on here?"

Yes. It is very simple: you need to learn about the practical limits of floating point numbers:

http://www.mathworks.com/help/matlab/matlab_prog/floating-point-numbers.html

http://www.mathworks.com/matlabcentral/answers/69-why-does-1-2-3-1-3-not-equal-zero

http://matlab.wikia.com/wiki/FAQ#Why_is_0.3_-_0.2_-_0.1_.28or_similar.29_not_equal_to_zero.3F

http://www.mathworks.com/matlabcentral/answers/57444-faq-why-is-0-3-0-2-0-1-not-equal-to-zero

http://www.mathworks.com/company/newsletters/news_notes/pdf/Fall96Cleve.pdf

http://www.mathworks.com/matlabcentral/answers/41536-why-is-2-24-10-22-4-not-equal-to-0

https://www.mathworks.com/matlabcentral/newsreader/view_thread/66553

http://www.mathworks.com/company/newsletters/news_notes/pdf/Fall96Cleve.pdf

http://blogs.mathworks.com/loren/2006/08/23/a-glimpse-into-floating-point-accuracy/

http://www.mathworks.com/help/fixedpoint/ug/floating-point-numbers.html

And some external links on this topic:

http://www.lahey.com/float.htm

http://matlabgeeks.com/tips-tutorials/floating-point-comparisons-in-matlab/

Answer 1

[Fangjun Jiang]

This is really a floating point data precision issue. Run this to find out and deal with it based on whatever your use case.

isequal(3*0.3, 0.9)